11 toward the emitting surface could be small. Further, when θ 1 equals 90°, the reflection dot is not realized. Further, when θ 2 exceeds 60°, the transparency of the light guide plate 1 could be decreased, which is not preferable.

Note that the maximum cambers L1 and L2 of the curved sloped surfaces 11 and 12 are approximately given by the following:

L
⁢
1

=

d
·
tan

⁢

θ
⁢

1

L
⁢
2

=

d
·
tan

⁢

θ
⁢

2

Therefore, the pseudo half-spindle type reflection dot 1a can be represented by four parameters W, d, L1 and L2 and the condition L1>L2.

FIG. 3 is a diagram for explaining the effect of the light guide plate of FIG. 1.

As illustrated in (A) of FIG. 3, the curved sloped surface 11 serves as an effective region of the reflection surface of the light R1 from the light source 200, while, since the curved sloped surface 12 is located opposite to the light source 200 so that the light R1 of the light source 200 is hardly incident to the curved sloped surface 12. Thus, the curved sloped surface 12 serves as an invalid region; however, since the curved sloped surface 12 is smaller than the curved sloped surface 11, the invalid region is small. Also, as illustrated in (B) of FIG. 3, there is no side surface like the triangular type reflection dot 101. Therefore, the utilization of the light R1 of the light source 200 is high, i.e., the efficiency of taken-out light is high. Further, the number of linear constituent elements is smaller than that of the triangular type reflection dot 101, moire is hardly generated on the LCD panel 300.

Also, since there is no circular bottom surface 1021 as in the round type reflection dot 102a, the occupied area of the pseudo half-spindle type reflection dot 1a is small. Therefore, by forming the pseudo half-spindle type reflection dot 1a whose occupied area is smaller than the round type reflection dot 102a, the luminance of the light guide plate is maintained at an equivalent level as that of the prior art light guide plate where the round type reflection dot 102a is formed, a light guide plate having a high transparency can be realized.

Also, as illustrated in (B) of FIG. 3, particularly, when the light from the light source 200 has multiple light paths R1a, R1b and R1c, the light paths R2a, R2b and R2c towards the LCD panel 300 are controlled to be diffused, the luminance fluctuation can be decreased.

FIG. 4 illustrates the arrangement of the pseudo half-spindle type reflection dots on the light distribution controlling surface side of the light guide plate 1 of FIG. 1, where (A) is a plan view, (B) is a graph showing the change of the Y-direction pitch, and (C) shows the Y-direction pitch.

In (A) of FIG. 4, when multiple pseudo half-spindle type reflection dots 1a are arranged, the X-direction pitch P_Xis at a definite value such as 0.154 mm while the Y-direction pitch P_Yis gradually decreased to increase the dot density since the light R1 of the light source 200 is weakened from the light incident surface S_into the counter light incident surface S_in′. Thus, the light R1 is made uniform from the light incident surface S_into the counter light incident surface S_in′. In this case, the X position of one dot is shifted by ΔX so the one dot that is not superposed onto another dot ahead of the one dot in the Y direction. Note that the pseudo half-spindle type reflection dots can be in a staggered arranged. Also, instead of changing the Y direction pitch P_Y, the Z direction depth d of the pseudo half-spindle type reflection dots 1a or the maximum camber L (=L1+L2) can be changed. To prevent local changes in luminance characteristics, the pseudo half-spindle type reflection dots are deformed to maintain their analogous shape when the Z direction depth d or the maximum camber L is changed.

FIG. 5 is a diagram for explaining simulations of the comparison in luminance between the round-type reflection dot of FIG. 13 and the pseudo half-spindle type reflection dot of FIG. 1, where (A) shows light distributions of emitted light from the light incident surface S_into the counter light incident surface S_in′, (B)-1 shows the Z-direction depth d=4 μm of the round-type reflection dot 102a of FIG. 13, (B)-2 shows the Z-direction depth d=4 μm of the pseudo half-spindle type reflection dot 1a of FIG. 1, (C)-1 shows an arrangement of the round-type reflection dots 102a in the light guide plate of FIG. 13 viewed from the plan side, (C)-2 shows an arrangement of the half-spindle type reflection dots 1a in the light guide plate of FIG. 1 viewed from the plan side. In (B)-1 and (B)-2 of FIG. 5, the Z-direction depth of the reflection dots is the same. When comparing for an interval from the location 20 [mm] to the location 170 [mm] from the light incident surface S_in, which is a section where the luminance of the light guide plate is approximately the same, the pattern area A [mm²] per one reflection dot was 7.68×10⁻⁴[mm²] in the case of the round-type reflection dot 102a from (C)-1 of FIG. 5, and the pattern area A [mm²] per one reflection dot was 1.39×10⁻⁴[mm²] in the case of the pseudo half-spindle type reflection dots 1a from (C)-2 of FIG. 5. Also, the number (N) of dots within the same pattern area (B=1574 [mm²] was 66563 in the case of the round-type reflection dot 102a from (C)-1 of FIG. 5, and was 225438 in the case of the pseudo half-spindle type reflection dots 1a from (C)-2 of FIG. 5. Therefore, the area ratio (the ratio of reflection dots occupying this area)=A×N÷B was 3.25% in the round-type reflection dot 102a and 1.99% in the pseudo half-spindle type reflection dots 1a. That is, as compared with the round-type reflection dot 102a, the pseudo half-spindle type reflection dots 1a has a higher light take-out efficiency per dot formation area and can realize a light guide plate with a higher transparency maintaining the luminance of the light guide plate at the same degree as the prior art.

As a manufacturing method of metal molds used in the manufacture of the light guide plate 1 of the pseudo half-spindle type reflection dots 1a, a super precision mechanical processing method mounts a diamond cutter tool on a piezoelectric element unit to form concave dots in a metal mold (see: Patent Literature 2). According to this method, since the surface of the reflection dot 1a can be made a mirror surface, it is possible to precisely control the light distribution by the pseudo half-spindle type reflection dots 1a. In addition, its manufacturing apparatus is inexpensive as compared with an apparatus using the photolithography processing apparatus.

FIG. 6 is a diagram for explaining a manufacturing method of the light guide plate of FIG. 1.

First, referring to a super precision roll mechanical processing step as illustrated in (A) of FIGS. 6 and (A) and (B) of FIG. 7, a cylindrical metal mold 601 plated with copper, brass or the like is rotated in a rotational direction F and a diamond cutting tool 602 is moved by a piezoelectric element unit (FTS) 603 along an up/down depth direction as indicated by an arrow shown in (B) of FIG. 7, so that a concave dot corresponding to the pseudo half-spindle type reflection dot 1a is formed. Thus, a concave dot metal mold 601 is obtained. Instead of the diamond cutting tool 602 and the piezoelectric element unit 603, a processing machine such as a precision lathe and a precision plate cutting unit can be used.

Next, referring to (B) of FIG. 6 which shows a resin sheet inverting step, a dot inversion is carried out by using the concave dots of the concave dot metal mold 601 as a parent to obtain a convex dot resin sheet 604.

Next, referring to (C) of FIG. 6 which shows an electroforming inverting step, an electroforming inversion is carried out by using the convex metal mold 604 as a parent to obtain a concave dot resin sheet 605.

Next, referring to (D) of FIG. 6 which shows an electroforming inverting step, an electroforming inversion is carried out by using the concave dot resin sheet 605 as a parent to obtain convex dot resin sheets 606. Note multiple convex dot resin sheets 606 realize stampers (mass-production patterns).

Next, referring to a roll metal mold forming step as illustrated in (E) of FIG. 6, a metal mold is wound by the convex dot resin sheets 606 to obtain a convex dot metal mold 607.

Finally, referring to (F) of FIG. 6, multiple pseudo half-spindle type reflection dots 1a are simultaneously formed by the convex dot metal mold 607 on the light distribution controlling surface S_contof the light guide plate 1.

According to the manufacturing method as illustrated in FIG. 6, the concave dot surface of the concave dot metal mold 601 is made a three-dimensional mirror-surface by the fine cutting due to the diamond cutting tool 602, so that the pseudo half-spindle type reflection dot 1a also has a mirror surface by using the concave dot metal mold 601, thus precisely distributing the light. Also, since the diamond cutting tool 602 can be reciprocated along the depth direction by the piezoelectric element unit 603, so that a concave dot can be engraved by the diamond cutting tool 602 at a high speed in the metal mold 601. Thus, a concave dot process can be performed upon the metal mold 601 in a short time.

FIG. 8 is a diagram for explaining the light distribution of the light guide plate of FIG. 1, where (A) shows a polar coordinate representation, and (B) shows a two-dimensional representation.

As illustrated in FIG. 8, while the angle θ2 of the curved sloped surface 12 is fixed at 10°, the angle θ1 of the curved sloped surface 11 is changed at 55°, 58°, 60° and 65°, thus changing the light distribution. Particularly, in the manufacturing method, the angle θ 1 of the curved sloped surface 11 can be changed by changing the edge tool angle of the diamond cutting tool 602 or the direction of the diamond cutting tool 602 perpendicular to the cutting direction, thus changing the light distribution. As a result, as occasion demands, the efficiency of the back-light can be changed. In any case, the light distribution is excellent as compared with the light distribution using the round-type reflection dot 102a.

For example, the larger θ 1, the larger the light distribution characteristics to the counter light incident surface S_in′. When the eye point is set closer to the counter light incident surface S_in′ than the center of the light guide plate along the Y-direction, θ 1 is made larger to increase the amount of the reflected light R2 on the side of the counter light incident surface S_in′, thus improving the visibility of the display apparatus at the eye point. In any case, the light distribution is excellent as compared with the light distribution using the round-type reflection dot 102a.

On the contrary, when the eye point is set closer to the light incident surface S_inthan the center of the light guide plate along the Y-direction, θ 1 is smaller to increase the reflected light R2 on the light incident surface S_in, thus improving the display apparatus at the eye point.

Preferably, since the larger θ 1, the higher the reflectivity, when an expected eye point is deviated from the center of the light guide plate along the Y-direction, the positions of the light source 200 and the light incident surface S_inare set on an opposite side of the eye point along the Y-direction, to improve the utilization of light.

Also, the angle θ 1A of a reflection dot of the curved sloped surface 11 near the light source along the Y-direction is set to be large, the angle θ 1B of a reflection dot of the curved sloped surface closer to a region immediate below the eye point along the Y-direction is made smaller than θ 1A, and the angle θ 1C of a reflection dot of the curved sloped surface in a region behind the region immediate below the eye point along the Y-direction is made smaller than θ 1B. Thus, the light distribution can be focused toward the eye point of the display apparatus.

On the contrary, the angle θ 1A of a reflection dot of the curved sloped surface 11 near the light source along the Y-direction is set to be small, the angle θ 1B of a reflection dot of the curved sloped surface closer to a region immediate below the eye point along the Y-direction is made larger than θ 1A, and the angle θ 1C of a reflection dot of the curved sloped surface in a region behind the region immediate below the eye point along the Y-direction is made larger than θ 1B. Thus, the visible angle can be increased.